1. Field of the Invention
The present invention relates to a method of producing a semiconductor device, a solid-state imaging device, a method of producing an electric apparatus, and an electric apparatus.
2. Description of the Related Art
Isolation using an impurity diffusion layer is a technology of isolating a unit pixel in a solid-state imaging device such as a CCD imaging device. When an n-type photosensor including a photodiode forms a unit pixel, a lattice-shaped p-type impurity diffusion layer is formed as an element isolation region isolating unit pixels from one other. Such an element isolation region is formed by ion implantation between unit pixels through an ion implantation mask.
A unit pixel has been reduced in size in recent years. Accordingly, in order to increase a photosensor area for increasing an amount of light incident on each photosensor and increasing sensitivity of an imaging device, a deep and narrow element isolation region is demanded.
A certain amount of ion implantation energy may be necessary to ion implant an impurity between unit pixels and form a deep element isolation region. This increases an aspect ratio which may be necessary to form an opening in an ion implantation mask (hereinafter II mask). Currently, an II mask structure having a desired high aspect ratio may not be obtained using a photoresist as a mask material. Therefore, RIE (reactive ion etching) is typically used to form an II hard mask of SiO2 having a desired structure.
FIGS. 1A to 1C are schematic process views of a method of producing a solid-state imaging device using an II hard mask in the related art. This example illustrates a schematic process of forming an element isolation region in a solid-state imaging device, where the element isolation region is formed by ion implantation.
First, as shown in FIG. 1A, an SiN film (hereinafter P—SiN film) 21 by plasma CVD (chemical vapor deposition), an SiO2 film 22 and a resist mask 23 are formed on a surface of an Si substrate 20 with an n-type photosensor formed thereon, for example. Here, the photosensor formed on the Si substrate 20 is not shown. The P—SiN film 21 formed on the Si substrate 20 is used as a stopper layer, and the SiO2 film 22 is used as an II hard mask. The SiO2 film 22 forms an II hard mask having a high aspect ratio and thus has a thickness of 5 μm, for example. The resist mask 23 is formed as a pattern having a slit-like opening 25 formed by pattern exposure and development. Here, the opening 25 is formed to have a width of 0.5 μm, for example.
Next, as shown in FIG. 1B, the SiO2 film 22 is etched through the opening 25 of the resist mask 23 to form an II hard mask 26 having a high aspect ratio.
Next, as shown in FIG. 1C, a p-type impurity, for example, is ion implanted into the Si substrate 20 through the II hard mask 26 having a high aspect ratio and thermally diffused to form an element isolation region 24. Since an impurity is ion implanted into the Si substrate 20 through the II hard mask 26 having a high aspect ratio, a narrow and deep p-type diffusion region may be formed as the element isolation region 24.
In addition to a demand for a pixel reduced in size, an element isolation region is also demanded to be narrow, and therefore an II hard mask opening is demanded to be as narrow as 0.3 μm or less. FIGS. 2A to 2C show a schematic configuration of a solid-state imaging device having an II hard mask having an aspect ratio of 20, for example. In FIGS. 2A to 2C, parts corresponding to those of FIG. 1 are indicated by the same symbols and repeated description thereof is omitted. In the case of forming the II hard mask 26 as shown in FIGS. 1A to 1C, it is difficult to vertically process the SiO2 film by RIE when the aspect ratio reaches about 20. In this case, the II hard mask 26 may not have an ideal vertical shape as shown in FIG. 2A but has a tapered shape as shown in FIG. 2B or a bowing shape as shown in FIG. 2C. When the opening of the II hard mask 26 has a tapered or bowing shape, ion implantation is performed in accordance with a widest width of the opening shape. Therefore, distribution of an impurity diffusion layer is wider than a desired distribution indicated by a broken line as shown in FIG. 2B or 2C. Accordingly, in the solid-state imaging device, the element isolation region 24 becomes wider than the desired distribution region indicated by the broken line and narrows an adjacent photosensor region (not shown), so that sensitivity of the imaging device to incident light is decreased, disadvantageously.
Japanese Unexamined Patent Application Publication No. 9-162137 discloses an ion implantation method including reducing a size of an opening on a lower edge of the opening of a mask pattern by reflowing to control a minute area of an ion implantation region and then implanting ions in a desired position.